Due to the costs involved in manufacturing semiconductor devices and various other factors, such devices are typically manufactured en masse on a semiconductor wafer, e.g., a silicon wafer. A single silicon wafer may hold hundreds or thousands of semiconductor devices. After semiconductor processing operations are complete, the wafer may be cut apart, or “diced,” to separate the individual semiconductor devices. The resulting semiconductor devices are called “dice,” or, in the singular, a “die.”
Due to the fact such dice are quite fragile and have feature sizes that are still quite small, it is common practice to affix a die to a package substrate to form a semiconductor package which is then sold to manufacturers of electronic devices. The package substrate is larger than the die in area and provides, among other things, structural support to the die as well as an electrical interface that serves to connect electrical contacts on the die side with electrical contacts on the opposing side that are typically larger and more widely-spaced. For example, one common way to mount a semiconductor package is to use flip-chip ball-grid-arrays (BGAs). In a BGA, a pattern of solder balls, usually a square array (often hollow in the middle), is affixed to the underside of a package substrate. Each solder ball is affixed to a contact pad on the underside of the semiconductor package. The contact pads, in turn, are electrically connected with solder bump pads on the opposing side of the package substrate through a number of conductive layers and vias within the package substrate; the solder bump pads are spaced and sized so as to connect with corresponding contact pads on the die using solder bumps. To install a BGA semiconductor package, the semiconductor package is positioned over corresponding contact pads on a printed circuit board (PCB) or similar component and then heated above the solder re-flow temperature. The solder balls then melt and, through surface tension, automatically center the semiconductor package over the contact pads on the PCB. When the solder balls cool, they form the electrical and structural connections between the semiconductor package and the PCB.
Discussed herein are techniques and structures for use in the design of package substrates for semiconductor devices.